Electromechanical translating device



Jan. 18, 1938. o. .M. DUNNING ELECTROMECHANICAL TRANSLATING DEVICE 2 Sheets-Shet 1 Filed Dec. 6, 1935 [N VENTOR 071/11? 711. Dunning A TTOYRNE y Jan. 18, 1938. Q DUNNING 2,106,051

ELECTROMECHANICAL TRANSLATING DEVICE Filed Dec. 6, 1955 2 Sheets-Sheet 2 INVENTOR pkgzijfiw 1/! TTORNE Y In the older forms of such machines, it has cutting two thin slabs or sections from a homov45 mounted in asmall stylus arm which was pivotally and in which the depth of the groove engraved Patented .lsl la, 193s r r 2,106,051

UNITED STATES PATENT OFFICE ELECTROMECHANICAL TKANSLATING DEVICE Orville M. Dunning, East Orange, N, J., assignor to Thomas A. Edison, Incorporated, West Orange, N. 1., a corporation of- New Jersey Application December 6, 1933, Serial No. 701,247 20 Claims. (Ci. rill-100.41)

My invention relates to electromechanical tainedis usually much poorer than the charactranslating devices and more particularly to electeristic which would be obtained if the translattrical phonographic recorders which are adapted ing device couldebe so mounted as to vibrate the to be used on recording machines andwhich, by stylus directly. I

5 reason of the nature of the uses to which they I have found however that there is one type are put, must not only be extremely rugged but of translating device which is particularly also must not require any appreciable adjustment. adapted for use in these electrical recorders beafter they have been put into service. An example cause it has a much higher ratio of sensitivity to of such use is the dictating machine of which perweight than any of the other devices with which sons who have no understanding of the mecha- I am familiar. This device is a special form of nism are the most frequent users and in respect piezoelectric crystal, such as that described in of which the manipulation of a few simple con- U. S. Patent No. 1,802,782, issued to C. B. Sawyer v trols must be the entire extent of the attention on .April 28, 1931, and entitled Piezo-electric derequiredto be given to the machine by the user. vice. Such a translating device is formed by been common practice to employ a vibratable diageneous Rochelle salt crystal, cementing these phragm carrying a sapphire recording stylus, the two sections together with an intervening elecdiaphragm being held in an extremely lightweight trode of tinfoil or similar material, and cementpivotally mounted sound box. Such stylus is ing electrodes to the outer surfaces ofthe two thus movable toward and away from the record crystal sections, substantially parallel with the tablet and in normal operation bears against center electrode. -The'two outer electrodes of the record tablet with a pressure, due to the efthe crystal device so formed are connected tofective weight of the sound box, which is made gether. when a voltage is applied to this crystal just sufficient to cut the desired depth of groove. device by connecting the center electrode to one 5 This general arrangement has been used in prac-' side of the source of the voltage and the two tically all commercial dictating machines for outer electrodes to the other sideof the source, a many years and has proven entirely satisfactory field is applied to the two sections of crystal in for this type of recording. opposite directions with the reslt that one of said However, it. has usually been found somewhat sections will tend to increase in length and the 30 difiicult to construct electrical recording devices other of said sections to decrease in length. This 30 in which this same general arrangement of parts results in a bending action similar to that exis used. Most practicaltypes of electromechanihibited by bi-metallic strips when heated. With cal translating devices do not lend themselves to such a construction, a much greater deflection the reduction of weight required by such an armay be obtained than with a single piezoelectric :7, rangement. In general, these devices cannot be crystal element. Such'a translating device is 5 reduced in weight to the point required by said therefore extremely well suited for main elecarrangement without rendering them almost trical recorders wherein the stylus is actuated completely insensitive. For this reason most of directly by the translating device since the crysthe electrical recording devices t fore detal material is light and relatively small sections 40 signed for operation in the service referred to thereof may b used. 40 above, were arranged so that the translating 11; is therefore the principal object of my indevice was mounted on a carriage suppor 111- vention to provide an electrical recorder in which place over a record tablet support. The engravthe recording tylus i applied directly to the. ing of the record was accomplished by a stylus translating device t t intervening linkages supported by a light frame, which frame, in turn, h Wei ht and was pivotally mounted on the, carriage; and the gf fzg f fgif f gg'fifggfg zl z i 8 stylus was connected to the translating device It is aiurther object of my invention to prob i y means 0 a lmk so as to permit free motion vide an electrical recorder wherein the translatso of the stylus arm toward and away from the rec- 0rd tablet. Practically all of these devices are device is plemlectric crystal the unsatisfactory because it is difiicult to prevent bending rattles in the link connection without introduc- It 15 another Object my inventmn to Provide ing undue restraint, and because, with s ch an an electrical recorder utilimng a piezoelectric arrangement, the frequency characteristic obcrystal as a translating medium in which the tal unit crystal is well protected against damage due to mishandling or to shock.

It is a further object of my invention to provide an electrical recorder in which the stylus is carried directly by a translating device mounted for movement toward and away from the record tablet and wherein a novel construction is provided to permit connection of the recorder to an outside source of electrical sound vibrations without the use of flexible wire connections.

It is still another object of my invention to provide a suitable electrical circuit in which the crystal unit recorder may be made to operate correctly.

Further objects and features of my invention will appear in the following specification and appended claims.

For a clearer understanding of my invention, reference may be had to thedrawings accompanying and forming part of this specification, wherein:

Figure 1 is a side elevational view of a portion of a recording machine including an electrical recorder embodying a preferred form of my invention.

Fig. 2 is a sectional view taken approximately on the line 2-4 of Fig. 1;

Fig. 3 is a bottom plan view of the frame of the recorder and certain associated parts;

Fig. 4 is a sectional view taken approximately on the line 4-4 of Fig. 2, of the translating device assembly;

Fig. 5 is an enlarged perspective view showing various parts of the translating device assembly, and

Fig. 6 is a diagram showing the electrical circult of the recorder.

The recording machine comprises a carriage i mounted for sliding movement on a guide rod 2. The carriage is moved by any suitable means such as a feed screw (not shown) transversely or a record tablet A which may be rotated during recording by any suitable means. The recorder is mounted on the arm i and comprises a frame 3 to the under side of which is secured a block of insulating material t5. A pair of brackets 5 and 5 are held in place on the block 4 by screws 5 and 6' which are insulated from the frame 3 by suitable insulating washers and bushings. The brackets 5 and it serve as-a support for the re corder unit as well as for the bringing out of electrical connections from such unit.

The recorder unit includes a piezoelectric crystal bending unit 1 of the type described in the above mentioned U. S. Patent No. 1,802,782, issued to C. B. Sawyer on April 28, 1931. This unit comprises two sections cut from a homogeneous Rochelle salts crystal, the sections being cemented together with an intervening central electrode 1 to which one connection is made. The crystal sections are also provided with a pair of outside electrodes 1', these two electrodes being connected together to form the other connection to the crystal unit. -At one end the crysis cemented into a, suitably-formed channel in a block I of suitable insulating material, such as bakelite. A pair of holes I are drilled in the block l and intersect the'channel which carries the crystal unit to provide for bringing out the leads from the electrodes of the crystal unit. The lead from the center electrode passes through one of these holes and the leads of the two outside electrodes pass through the other of these two holes. The block I is also drilled at right angles to the holes I to receive also suitably drilled and a pair or pivots II which are provided with slots ll attheir inner ends and are slightly flattened at the top. These pivots intersect the holes 9 through which the leads from the crystal unit electrodes pass and in consequence, when they are inserted, the leads are pushed into the slots ll formed on theirinner ends. The block is tapped to receive a pair of screws H. These screws when tightened serve to clamp the split ends of the pivots II and thereby make a secure connection to the leads from the crystal electrodes. It will thus be seen that connections may be made. to the electrodes of the crystal unit through the pivots III which are insulated from each other.

At the end opposite to that cemented in the block 8, a clip' i 2 is cemented to the crystal unit. A stylus holder I3 is suitably secured to this clip by means of screws, and carries a stylus H.

The entire crystal unit assembly is enclosed in a case of strong aluminum alloy comprising a top section ii, a bottom section l8, and a rear section 23. This case is held in place by suitable screws I! threaded into the bakelite block 3. The 7 lower portion l6 of the case is suitably cut out to allow passage of the stylus holder l3. Between the crystal unit and the enclosing casing, a pair of rubber blocks or pads i8, substantially co-extensive with the unencumbered portions of the -crystal unit faces, are disposed under considerable compression.

Theconical ends of the pivots l0 are adapted to iii; in a pair of suitably drilled holes I9 in the brackets 5 and 6. I'he bracket 5 is made somewhat springy to permit insertion of the pivots i0.

An adjusting screw 10, threaded into the bracket 6 and insulated from the bracket 5 by a suitable insulating bushing and washer, is provided in order to adjust the tension which is applied upon the pivots of the device. For proper adjustment, this screw is set so that there is substantially no play in the pivots, but so that they are not sumciently tightly clamped to cause any binding of the translating device assembly which might prevent the recorder stylus freely following the irregularities o: the record. The pivoted translating device assembly is also provided with a fin 2! arranged for coaction with a narrow cup 22 carried by the bracket 8. This comprises a stabilizing means and is explained in detail in my 00- pending application Serial No. 659,743, now U. S. Patent No. 2,028,197.

The circuit with which the device is used is shown in Fig. 6. The leads from the recorder are connected to an amplifier with a resistance R in series.

In the construction outlined above, it is ob vious that if the connections mentioned are made to the terminals 5 and 6' from a source of voltage such as a thermionic amplifier, this voltage will be applied across the sections of the crystal unit by reason oi the connections through the brackets 5 and 6, the pivots l0, and the leads of the crystal unit. By making the connections to the pivots in this way undesirable loose leads are dispensed with thus making it simple to assemble and disassemble the translating unit in respect of the supporting brackets without disconnecting any wires. Furthermore, because of the high impedance oi the crystal unit itself which may be a substantially pure capacity 0! approximately .0025 mid, any slight irregularity in a pivot resulting in a somewhat imperfect contact between the pivot and the bracket ll, would have negligible efl'ectppon the systamsince in 7 two things:

no case. would the contact. resistances rise to, values comparablewith the impedance of the crystal unit.

It will also be noted that in the construction shown, the crystal unit is cemented into the holder at a point very close to the pivot so that this end of the crystal unit isv held securely against translatory movement. Therefore, the maximum deflection of the crystal will-occur at the end of the crystal carrying the stylus, thus providing maximum sensitivity.

The case l5, 16 about the crystal unit provides a certain amount of protection to such unit which is somewhat fragile and might be easily broken if it were exposed. The protection of the crystal unit is further increased by the inclusion of the rubber blocks or pads i8 between the case and the unit. These pads are placed under some compression and accordingly provide considerable additional support for the crystal unit, thus overcoming almost entirely the danger of breakage of the latter due to its fragility. The rubber pads l8 however have two additional functions which are extremely important in con- 1 nection with the recorder herein disclosed. The first of these is that they serve to increase the effective stiffness of the crystalunit, thereby in-- creasing its fundamental resonant frequency and increasing the range of frequencies which may be recorded. In addition, they provide a certain amount of viscous damping which'serves to considerably decrease the response of the crystal unit at resonant frequencies and thereby to make the response characteristic of the recorder more uniform than might be obtained without their use.

In the structure which I have so particularly described and illustrated it will be seen that the mass of the crystal unit forms a substantial portion of the total downward biasing force on the stylus. .Thus the inherently high sensitivity per unit weight of the crystal proper, hereinabovementioned, is not unduly sacrificed and in the complete recorder an excellent ratio of sensitivity to weight is retained; thus obviously there is permitted a full modulation of the bias (and hence of the record groove) by modest alternating voltage inputs.

Particular attention is directed to the use of the resistance R in series with the crystal unit during recording. This resistance serves to do (1) to modify the frequency characteristic of'the recorder so groove of the type best suited for reproduction with ordinary phonographicreproducers, and (2) to hold the impedance of the combined output circuit comprising the crystal unit and the resistance, much more nearly constant than would be the case if the crystal unit alone were used. The amount of deflection which occurs in a piezoelectric crystal unit is a function only of the voltage which is applied to'the unit. It is nearly independent of the frequency of the applied voltage up to the fundamental frequency of resonance of the crystal, unit, over which range the compliance reaction due to the stiffness of the unit is much larger than the mass reaction. It is to be understood that if subjected to a frequency higher than'that where the fundamental resonance occurs, the response of the crystal unit may be very irregular since it tends to break up and to vibrate in parts.

It is therefore desirable that the fundamental resonance of the crystal unit should be made as high or slightly higher than the highest frequency to be rethat it cuts a record corded. The value of this resonant frequency is determined by the dimensions of the crystal unit and by its mounting. In my embodiment, I contemplate making the dimensions of the crystal such that the resonant frequency is at or above the highest frequency to be recorded. For these reasons if a sinusoidal voltage'of constant amplit'ude at a number of frequencies throughout the range ;to be recorded is applied to the crystal unit, the maximum cyclic displacement of the crystal unit would be substantially constant throughout the range. If such a condition existed in a recorder it would produce a record which has been called the constant amplitude type.

It has been well established in the art that the constant amplitude type record would introduce certain difficulties which would make it almost impossible to reproduce the higher frequencies in the range. siderations, it is generally accepted that the best type of phonographic record is that which is known as the constant velocity type in which the product'of the maximum cyclic amplitude at any frequency and the frequency is a constant. or in which, in other words, the maximum cyclic amplitude is inversely proportional to the fre quency. By the inclusion of a resistanceof the proper value in series with the crystal unit, such a characteristic is obtained when a constant volt- ;age is applied to the combination of the resistance and the crystal unit. The impedance of the crystal unit is substantially that of a pure capacity so that its impedance continually falls with increasing frequency. in series with the crystal unit .a resistance which is of the same order of magnitude as the impedance of the crystal unit at the lowest frequencies to be recorded and if we apply constant voltage across the crystal unit and resistance, the voltage appearing across the crystal will be substantially inversely proportional to the frequency. As a result the amplitude of vibration of the crystal will be substantially inversely proportional to frequency, thus yielding a constant velocity type recording.

However, in some cases it is desirable, in order to get the maximum amount of recording upon a record blank for a given set of groove dimensions, to make the recorder response characteristic substantially constant amplitude below 300 cycles and constant velocity above 300 cycles. 1 accomplish this, where desired. by so proportioning the series resistance relative to the impedance of the crystal unit that at frequencies below I.

300 cycles; the resistance is less than the impedance of the crystal unit while above 300 cycles the impedance of the crystal unit is less than that of the resistance. In this way a record which approximates the constant amplitude characteristic below 300 cycles and the constant velocity characteristic above 300 cycles is obtained.

The use of a series resistor has one'other additional important function in this connection. It has been well established that there is a certain value of impedance into which the power output stage of the thermionic amplifier should work in order to obtain the minimum amount of distortion. This impedance is constant for all frequencies and therefore should be a substan- It is always possible of desired magnitude of reof a thermionic amplifier Howtially pure resistance. course to realize any sfstance in the output by the use of appropriate transformers.

ever it is essential that,

if minimum distortion For this reason and for other con- Therefore, if we, place I:

having a plurality of electrodes an from the amplifier is to be obtained, the output impedance should not vary greatly from the best value. It is obvious that by including a resistance in series with the crystal unit equal in value to the impedance of the unit at or near the lowest frequency in the range to be recorded, the variation in impedance in the ,output circuit is enormously decreased over that which would be obtained without the use of the resistance. While the impedance of the crystal unit falls off rapidly with frequency, the resistance remains constant so that the maximum possible deviation from the impedance in the output circuit at the frequency at which the crystal unit and resistance are matched is somewhat less than 40%.

In contrast to this, if the crystal unit only were included in the output circuit, a change of ten times in frequency would produce a-change of ten'times in output impedance so that this arrangement would be undesirable for use in corn nection with a thermionic amplifier.

Having thus described my invention, I claim: 1. An electro-mechanical translating device comprising a frame, a piezoelectric bending unit comprising a plurality of electrodes, a mounting for said unit, and a pivotalconnection between said mounting and said frame the axis of ca connection being substantially parallel to electrodes.

2. In an electrical recorder, a frame, a pieceelectric bending unit comprising a plurality of electrodes, a mounting for said unit, a pivotai connection between said mounting said frame, the axis of said connection suhstantially parallel to said electrodes-and record en;= graving means connected to J 3. An electro-mechanicai transiat device comprising a frame, a piezoelectric bending mounte on said frame for free rotary mover: axis parallel to said electrodes one end of said unit, and meal vibrations connected to s mote from said "her 4. An electro-niechanicai translat dev comprising a frame, a translating medium coiziprising an active eiernent adapted to upon the application of voltage thereto, and cantisaid element pivotally connected to said e adjacentone end of element for mov cnt of said translating medium in the direction of said lzen 5. In an electrical recorder, a name, a piezoelectric bending unit, a cantilever mounting for said unit pivotally connected to said frame adjacent one end of said unit for movement of said unit in the direction of its bending, and record engraving means connected to said unit at a point remote from said mounting.

6. In an electrical recorder, a piezoelectric bending unit and means for mounting said unit for movement about an axis adiacent one end or said unit, said unit being arranged for bending in the direction of said movement, and record engraving means carried by said unit.

lever mounting f 7; An .electro-mechanical translating device comprising a translating medium having an activeelement adapted for bending upon the application of voltage thereto. and means for mounting said medium for movement about an axis adjacent one end of said element, said elesaid unit anddevice toward and awe bias: a piezoelectric bending unit carry? element adapted for bending upon the application of voltage thereto, a solid cantilever mounting for said element pivoted to said frame for movement of said element toward and away from a record, said element being arranged in said mounting forbending in the direction of said movement, and record engaging means connected to said element.

9. In an electrical recorder including a device or engraving oscillations in a record, said device being adapted for bias against the record and being responsive to modulations of said bias: means for producing and modulating said bias comprising a piezoelectric bending unit carrying said device, supported for unitary movement toward and away from the record, and positioned for bending in the direction of such movement.

10. In an electrical recorder including a device for engraving oscillationsrin a record, said device being adapted for bias against the record and being responsive to modulations of said bias: means for producing and modulating said bias comprising a piezoelectric bending unit carrying said device, pivotally supported adjacent one vice for engraving oscillations in a record, said device being adapted for bias againstthe record and being responsive to modulations of aid bias:

means' forproducing and'modulating said bias comprising a piezoelectric bending unit carrying said device, and acantilever mounting for said unit pivotally supported for movement 01 record, said unit being positioned in sea; mount ing for bending in the direction. ofsuch move ment.

in a room device being adapted for bias against the 0rd and being responsive to modulations of device above the record, supported movement toward and away from the record,

sitioned for bending in the motion of such movement, and having a in es which prcvies substantial portion of said a In an electrical recorc r including a device for engraving oscillations in a record, set device being adapted for bias against the recorcl and being responsive to modulations of sai bias: a piezoelectric bending unit carrying sal device above the record, and a cantilever moun ing for said unit pivotally supported for move-- ment of said unit and device toward and away from the record, said unit being positioned in said mounting for bending in the direction of I such movement and having a mass which provides a substantial portion of said bias.

14. In an electrical recorder including a device for engraving oscillations in a record, said device being adapted for bias against the record and being responsive to modulations of said bias: a piezoelectric bending unit carrying said device above the record, and a. casing carrying and protecting said unit and supported for movement toward and away from the record, said unit being positioned in said casing for bending in the direction of said movement and having a, mass which provides a substantial portion of said bias.

ment of such element, a mounting for said ele- 15. In an electrical recorder including a device for engraving oscillations in a record, said device being adapted for bias against the rec- 0rd and being responsive to modulations of said bias: a piezoelectric device above the record, a casing carrying said unit and supported for movement toward and away from the record, and means between said unit and casing to resist relative movement therebetween, said unit being positioned in said casing for bending in the direction of said movement and having a mass which provides a substantial portion of said bias.

16. An electro-mechanical translating device comprising a frame, a translating medium comprising an active element adapted to bend upon the application of voltage thereto, a cantilever mounting for said element, and a pivotal connection between said mounting and. said frame comprising electrical connections to said medium.

17. 'In an electrical recorder, a frame, a piezoelectric bending unit, a mounting for said unit, and a pivotal connection between said mounting and said frame, said connection comprising electrical connections to said unit.

18. An electro-mechanical translating device comprising a frame, a translating medium comprising an active element and wherein the translatory action is accompanied by bending movebending unit carrying said ment, and a pivotal connection between said frame and said mounting comprising electrical connections to said medium.

19. An electro-mechanical translating device comprising a frame, a translating medium comprising an active element and wherein the transment of such ment, and a pivotal connection between said frame and said mounting comprising a pair of coaxial pivots insulated from each other, a pair of pivot receiving members insulated from each other and adapted to coact respectively with said pivots, said pivots and pivot receiving members constituting a portion of the electrical circuit of said translating medium. I

20. In an electro-mechanical translating device, a frame, a translating medium comprising an active element and wherein the transiatory action is accompanied by bending movement of such element, a mounting for said element, a pivotal connection between said mounting and said frame comprising a pair of coaxial pivots insulated from each other, and an electrical circuit connected to said medium and comprising said pivots.

ORVILIE M. DUNNING. 

